Ink jet recording is a printing method in which ink droplets are sprayed and made to adhere to paper or another recording medium. Recent years have witnessed amazing advances in ink jet recording technology, to the point that ink jet recording has come to be used even in the field of high-precision printing, which used to be the exclusive domain of silver halide photography or offset printing. This has been accompanied by the development of ink jet recording media having high gloss comparable to that of photographic paper, art paper, and the like used in the fields of silver halide photography and offset printing. The recording media used in a high-gloss ink jet recording method such as this generally comprise an ink receiving layer containing a porous pigment such as silica and provided over a substrate such as paper or a film.
The inks used when letters and/or graphics are recorded on the above-mentioned recording media used in high-gloss ink jet recording methods are typically a water-based ink composition whose main component is water and which contain colorants, resin components, and various other additives. Either dyes or pigments can be used as colorants, but pigments are superior in terms of their weather resistance (resistance to light, gas, water, moisture, and so forth), so demand for these pigments has been rising recently, and development of pigment ink compositions that take advantage of the characteristics of pigments is underway. Water-based pigment ink compositions containing a resin component have also been used in order to enhance the fixability of the pigment to the recording medium.
However, recorded material includes portions of high duty, portions of low duty, and non-recorded portions. Accordingly, when information is recorded using a pigment ink composition containing a resin component, many ink droplets are sprayed onto the high duty portions, so there is a correspondingly greater amount of resin component discharged, and more resin component adheres, whereas the discharge amount of ink droplets is smaller in the low duty portions, so less resin component adheres there. Also, since no ink droplets are sprayed onto the non-recorded portions, no resin component adheres there. Specifically, the high duty portions have a high gloss because of their higher resin component content, whereas the low duty portions have a lower gloss, and the gloss is lower still in the non-recorded portions. The glossiness therefore varies as a result of the difference in the amount of resin component that adheres, and this is reflected in recorded material quality as gloss unevenness. This problem of gloss unevenness is particularly pronounced in recording media used in high-gloss ink jet recording methods so often employed in high-precision printing.
Also, a problem that occurred with conventional ink jet recording methods that employed an ink composition containing a pigment as a colorant was that the gloss of the resulting printed image varied greatly with the duty level, that is, there was a large ratio (maximum value/minimum value) between the maximum value and minimum value for the gloss of the printed image that could be obtained when the duty was varied. This gloss ratio could be quite pronounced, depending on the type of pigment in the ink composition, and the pigment concentration in the ink composition.
One possible way to eliminate this gloss unevenness is to impart gloss by overcoating the recorded image with a resin film after the recording operation, but this results in resin component also being supplied to high duty portions, which already exhibit sufficient gloss, so cost becomes a problem.
Although not intended to solve the above-mentioned gloss unevenness, various methods have been proposed as prior art in which an overcoat layer is provided. For instance, Japanese Laid-Open Patent Application H8-174989 discloses a technique whereby, after ink jet recording, a transfer overcoat layer whose main component is a thermoplastic resin and which has been melt transferred via a heat-resistance film over the ink receiving layer of a recording medium used for high-gloss ink jet recording is provided for the purpose of achieving a printed image with excellent image quality and weather resistance. Problems with this technique, though, are that the cost is higher, the film becomes wrinkled, air gets trapped between the recording medium and the film, and so forth.
Japanese Laid-Open Patent Applications H11-277724 and 2000-141708 disclose a technique in which an image produced by ink jet recording is coated with a UV-curing coating agent, and this coating is then irradiated with UV rays and cured, the purpose of which is to enhance the scratch resistance of a recorded image formed on a recording medium with no ink absorptivity, such as a product made from plastic or metal. Problems with this technique, however, were that the cost was high, the process was complicated, UV rays which are harmful to humans were used, and so on.
Also, Japanese Laid-Open Patent Application H11-263052 discloses a technique in which a solid transparent resin capable of forming a coating is heated and melted and discharged from a nozzle over a recorded image during ink jet recording, so that the recorded image is covered with this transparent resin. This technique, however, is not suited to ordinary ink jet recording methods because it presupposes a so-called solid ink jet recording method.
Further, even if this technique were applied to an ordinary ink jet recording method, since a coating is formed over the entire recorded image, an extremely large amount of the transparent resin is used, which drives up the cost, and the ink tank installed in an ordinary ink jet recording apparatus cannot hold all of the liquid transparent resin, so the apparatus has to be modified and made larger, among other such problems.
It is therefore an object of the present invention to provide an ink jet recording method and ink set with which recorded material with excellent weather resistance and greatly reduced gloss unevenness can be easily obtained without higher costs being entailed, the ink jet recording apparatus having to be modified or made larger, etc.
It is a further object of the present invention to provide an ink jet recording method with which a high-quality image can be obtained with a low gloss ratio (maximum value/minimum value) dependent on duty, as well as recorded material produced by this method.